This invention relates generally to metal alloys and more particularly to alloy compositions suitable for use in hot, corrosive, combustion atmospheres of the type found in gas turbines. Currently, the high cost of quality fuels for gas turbines has made it economically attractive to use lower quality fuels or to increase the temperature of the gas path of the turbine. These lower quality fuels may contain harmful alkali-sulfates which cause accelerated hot corrosion attack of the hot gas path components of gas turbines. These hot gas path components such as vanes and blades are generally constructed of nickel or cobalt base super alloys. The super alloys, while possessing high strength at high temperatures, are quite prone to the accelerated corrosive effects of the hot gas path.
Heretofore, attempts have been made to replace the super alloy components with corrosion-resistant materials, but these have been unsuccessful because the cast, powder metallurgical, and wrought alloys having the necessary corrosion resistance do not possess sufficient mechanical properties for service in the gas turbine environment. Heretofore, the most successful approach has been to coat the super alloy components with corrosion-resistant materials; however, these have not proven completely successful, either because the built-up or the diffusion types, are limited by coating defects, high brittleness or the great expense of certain platinum group metals. Another approach has been to clean the front end fuel or inlet air of corrosive elements; however, this has proven to be very expensive and lacks versatility to handle diverse fuels. Additives added to the fuels to mitigate the effect of corrosive elements are not only costly, but they result in heavy deposit formations in the hot gas path components of the turbine.
This invention solves many of the problems heretofore encountered in hot corrosive combustion atmospheres by providing an alloy which is highly resistant to hot corrosion attack and which also possesses a high degree of ductility.